The wheels of a two-wheeled vehicle such as a motorcycle or a scooter tilt as the vehicle is driven on a curve in a road if the driver of the vehicle shifts his weight into the curve. In fact, part of the enjoyment which the driver experiences from such a vehicle is the way the vehicle tilts as he shifts his weight into the curves of a winding road.
Vehicles having more than two wheels do not tilt in the same way. For example, a three-wheeled vehicle such as a motorcycle with a side-mounted wheeled-compartment for a passenger does not tilt as the vehicle rounds a curve unless the vehicle is travelling at an excessive speed. When the vehicle travels at such speed and it rounds a curve on the side opposite the passenger compartment, the wheels of the motor cycle tilt but as they do, the wheel of the passenger compartment lifts off the road. The vehicle then becomes unstable and difficult if not impossible to control.
Vehicles having four or more wheels generally do not respond to the shifting of a driver's weight because they are too heavy. If however the vehicle is light enough to respond, the vehicle too becomes unstable in the same way as a three-wheeled vehicle.